In recent years, image quality of ink jet recording materials has been rapidly improved to approach photographic image quality. Particularly, to achieve image quality comparable to photographic image quality via ink jet recording, improvement also with respect to an ink jet recording sheet (hereinafter, also simply referred to as a recording sheet) has also progressed, and a porous-type recording sheet, in which a tiny pore layer comprised of inorganic particles and a hydrophilic polymer is provided on a very smooth support, is becoming a recording medium resulting in the nearest photographic image quality, since it exhibits high gloss, vivid coloration, as well as excellent ink absorbability and drying characteristics. Particularly, when a non-water absorbing support is utilized, cockle after printing, so-called “wrinkles”, which are often observed with a water absorbing support, are not generated and a very smooth surface is maintained to result in a higher quality print.
Ink jet recording is generally classified into one which utilizes water-based ink using water and a water-soluble solvent as an ink solvent and one which utilizes a non-water based oil solvent, and each of these comprises a type which utilizes a dye as a colorant and a type which utilizes a pigment, which require an exclusive sheet suitable for each type to result in high quality images. As for ink, water-based ink with less environmental load and greater safety aspects has prevailed.
Among water-based inks, pigment ink exhibits high image durability, however, it is tends to vary gloss image-wise, rarely resulting in print quality similar to photographic images; on the other hand, in case of utilizing water-soluble dye ink, a color print comparable to a photographic image having high image visibility as well as uniform surface gloss can be obtained relatively easily.
However, in contrast to the water-soluble dye which provides images of high quality, it has been a problem in that image stability is poor compared to a pigment ink and exhibits significant fading by sunlight or even room-light, and also fading by such an oxidizing gas such as ozone present in ambient air. Particularly, a porous-type recording sheet provided with a tiny pore layer is sensitive to ambient oxidizing gas because the contact area between a dye and the air in a room is increased, and improvement has been desired.
In order to overcome such deterioration due to storage, many proposals have been made such as various kinds of anti-oxidants as anti-fading agents being added.
For example, an ink jet recording sheet including various kinds of compounds as anti-oxidants is described in JP-A Nos. 57-87989, 57-74192 and 60-72785; an ink jet recording sheet in which an UV absorbent is incorporated in JP-A No. 57-74193; addition of a hydrazine series in JP-A No. 61-154989; addition of a hindered amine type anti-oxidant in JP-A No. 61-146591; addition of a nitrogen containing. heterocyclic mercapto type compound in JP-A No. 61-177279; addition of a thioether type anti-oxidant in JP-A Nos. 1-115677 and 1-35479; addition of a hindered phenol type anti-oxidant having a specific structure in JP-A No. 1-36480; addition of a hindered phenol type anti-oxidant and a hindered amine type anti-oxidant in combination in JP-A No. 3-13376; addition of an ascorbic acid series in JP-A Nos. 7-195824 and 8-150773; addition of zinc sulfate in JP-A No. 7-149037; incorporation of a thiocyanate series in JP-A No. 7-314882; addition of a thiourea derivative in JP-A No. 7-314882; incorporation of a saccharide in JP-A Nos. 7-276790 and 8-108617; addition of a phosphoric acid type anti-oxidant in JP-A No. 8-118791; addition of such as a nitrite, a sulfite and a thiosulfite in JP-A No. 8-300807; and addition of a hydroxyl amine derivative in JP-A No. 9-267544.
However, in an ink jet recording sheet provided with tiny pores, the effect can hardly be said to be sufficient, and there is a problem in that ink absorbability of a porous layer is decreased when a large amount of such various anti-fading agents are added to achieve a sufficient anti-fading effect.
Further, in the case of utilizing water-soluble dye ink, problems such as disadvantages of generated bleeding and of poor water resistance exist, due to high hydrophilic characteristics. That is to say, dyes tend to bleed when stored under high humidity over a long duration after recording or if water drops are accidentally dripped onto a printed surface. To overcome this problem, it is a general practice that a dye fixing substance such as a cationic substance is added to the pore layer. For example, preferably utilized has been a method in which a cation polymer is utilized and which combined with an anionic ink dye to firmly immobilize the dye. Such cationic polymers include a polymer having a quaternary ammonium group, such as described, for example, in “Technologies and Materials for Ink jet Printer” (published by CMC Co., Ltd., July 1998) and the literature in paragraph [0008] of JP-A No. 9-193532. Further, a method, in which a water-soluble polyvalent metal ion is added into an ink jet recording sheet in advance on which dyes are immobilized by coagulating adhesion at the time of ink jet recording, is also proposed. Some reduction of bleeding and improvement of water-resistance are observed by use of a cationic polymer or a polyvalent metal ion, however, it is often the case that the effect cannot be exhibited sufficiently even with addition of aforementioned anti-fading agents having negligible diffusibility in an ink absorbing layer, because dye is unevenly distributed in an ink absorbing layer by bonding with a cationic polymer or a polyvalent metal ion.
On the other hand, it is known that resin having an unsaturated bond in a molecule such as butadiene rubber can be utilized in an ink jet recording sheet. For example, a method effectively utilizing resin mainly to absorb a solvent of oil-soluble ink is disclosed (refer to, for example, patent literature 1-6). Further, a utilization method, in which an absorbability of water-based ink is improved by sulfonation of a dien-type polymer or of a hydrogenation adduct thereof to be made hydrophilic, is disclosed, however, it has not been known heretofore that storage stability can be improved by use of a compound having an unsaturated bond in a tiny pore ink absorbing layer.